Species limits in the Black-headed Antthrush (Formicarius nigricapillus)

ARETA, JUAN I.; BENÍTEZ SALDÍVAR, MARÍA JULIANA

Journal of Ornithology

Springer

Año: 2025

2193-7192

The Black-headed Antthrush (Formicarius nigricapillus) inhabits humid to dry Neotropical forests with two allopatric subspecies: nominotypic nigricapillus in Costa Rica and Panama, and destructus in Colombia and Ecuador. Here we provide vocal, morphometric, and plumage data showing that F. n. nigricapillus (‘black-capped antthrush’) and F. n. destructus (‘black-hooded antthrush’) are better treated as separate species. Songs of both taxa are 100% diagnosable, without overlap in multivariate space, and with significant differences in 13 out of 15 acoustic variables. In comparison to destructus, the taxon nigricapillus showed lower peak frequency of notes, longer mean note duration and mean interval between notes, fewer notes per song, slower pace, and relatively even pace in the first and second halves of the song (versus deceleration in destructus). The song of nigricapillus encompasses ca. 490 km across Costa Rica and into C Panama whilst the song of destructus extends for ca. 1130 km from NC Colombia to SW Ecuador, with a known song-gap of ca. 190 km between them. The Río Atrato swamps in NW Colombia likely constitute the main biogeographic barrier separating these taxa. We show that nigricapillus exhibits longer bill and wings, and possibly a shorter tail (non-significant difference), chestnut-brown hindneck (sometimes extending to neck sides in a semicollar), and typically more chestnut-brown back, and conversely destructus exhibits shorter bill and wings, and possibly a longer tail (non-significant difference), all black hindneck and neck sides, and typically browner back.